The present invention relates to a rectangular-type headlamp for automotive use. More particularly, the invention relates to a rectangular automobile headlamp of the type in which a front lens has a stepped portion at an upper side edge portion so as to accent or emphasize the depth of the headlamp.
Recently, automobile headlamps of a rectangular shape, having a rectangular lamp body and a rectangular front lens, have become the dominant type of headlamps and have displaced round headlamps due to their improved appearance and for other reasons.
The present applicant has previously proposed to form a stepped portion at an upper side edge portion of a front lens a of a rectangular headlamp in order to accent the depth of the headlamp to thereby achieve a further novel appearance.
In automobile headlamps, however, in order to prevent fogging caused, for example, by condensation of water vapor on the inner surface of the lens or deposition on the inner surface of the lens of an oily film resulting from outgassing from hot rubber parts, air passages are provided in the lamp body for communicating the interior of the headlamp with the exterior atmosphere so as to cause a natural convection in the headlamp utilizing the heat generated by the associated bulb,
thereby to ventilate the interior of the headlamp.
The new concept of providing a stepped portion at the front lens has resulted in another problem that the natural convection in the headlamp is adversely affected thereby, resulting in a lowered ventilation efficiency. More specifically, as shown in FIG. 10, when a stepped portion 3 of a s uniform width is formed on the upper side edge portion of the front lens 2 along the edge thereof, an stagnant-air region 4 develops in the vicinity of a convex portion 3a on the inner surface of the lens. As a result, there has been encountered a problem that this stagnant region prevents a smooth natural convection flow, thus lowering the anti-fogging effect.
Reference numeral 6 in FIG. 10 denotes the lamp body.